the clients are all (outlook with zarafa-plugin, webapp, outlook 2013 with koe and mobile android) on the receiver side
and sending was done from a different external sites (exchange server with outloook 2016, kopano-server with webapp, koe and iphone)

but as i said when sending a meetingrequest from the site where the incoming meeting requests are 2h in front of local time the time i correct on the destination site

thanks for this hint - it could be the same - server was upgraded from UCS4.1 to UCS 4.2 and the UTC File is also wrong
I copied from different server too - don’t know if the server has to be restarted after that but will try this evening and give feedback afterwards